Irreversible transformation in as-cast FeAlB2-ordered alloy obtained by melt spinning

The aim of the work described in the present paper was to investigate the m icrostructural stability during annealing treatments of a Fe-Al alloy obtai ned by melt spinning. To this purpose internal friction (IF) and dynamic mo dulus (M-d) measurements were employed, and the results correlated with x-r ay diffraction, optical microscopy, and scanning and transmission electron microscopy observations. In particular, the B2-ordered Fe-38Al-2Cr-0.015C-0 .003B (in at.%) alloy was studied during repeated heating runs from room te mperature to 823 K by IF and M-d. The modulus exhibited a broad maximum (in the range of 600-800 K) only in the first run. On the basis of transmissio n electron microscopy and x-ray diffraction analysis, the irreversible tran sformation was explained by considering a two-stage process that occurs whe n vacancies in supersaturation move toward dislocations. The first stage is connected to dislocation locking; the second one is due to annihilation of some vacancies by dislocation climb.